Protection of rubber by stannous complex



water-soluble stannous salt of a strong acid, a

Patented Sept. 28, 1954 2,690,435

UNITED STATES PATENT OFFICE PROTECTION OF RUBBER BY STANNOUS COMPLEXHarry E. Albert, Akron, Ohio, assignor to The Firestone Tire & RubberCompany, Akron, Ohio, a corporation of Ghio No Drawing. Originalapplication April 4, 1949, Serial No. 85,473, now Patent No. 2,626,954,dated January 27, 1953. Divided and this application April 25, 1952,Serial No. 285,793

6 Claims. (Cl. 260-29.7)

1 2 This invention relates to the stabilization of The complexes may beproduced from a pherubbers and, more particularly, rubber-like conolicompound h s;

polymers of a conjugated diene monomer and Phen 01 a vinyl aromaticmonomer, typified by GR-S. p Tertiar octylphenol The conjugated dienemonomers which may be p cyclohgxylphenol used in such copolymers includebutadiene (by p Tertiary buty1pheno1 ig figg igg gfig 22 2333; Cresylicacid (a mixture of phenols derived from piperylene, dimethylbutadiene,2-methyl-l,3- 4 gf ffifggi ares o1 pentadiene, etc. The vinyl aromaticmonomers 1O tertiar y butyl-p cresol include styrene,nuclear-substituted styrenes, Salicylic acid alphamethylstyrene,monochlorostyrene, dioxy benzoic acid chlorostyrene, vinylnaphthalene,vinylbipheny p AminophenO1 vinylcarbazole, 2-vinyl-5-ethy1pyr dipmmwhenol -vinylpyridine, etc. The invention includes the Alpha aminobeta naphthol new stabilizers, their use in the rubber-like co- Alphachloro beta naphthol polymers, and the stabilized products. mchlorwhenolThe stabilizers most generally used with such p phenylphenol acopolymer, such as the well-known phenyl- 4 tertiary buty1 m wes01beta-naphthylamine, on aging discolor the c0- p Bromophenol polymer andlight-colored vulcanizates prepared Alphamaphthol from the copolymer.These light-colored vul- Bptamaphthol canizates are badly discoloredwhen exposed to Tgrtiary butyl beta naphthol ultraviolet light. Thestabilizers of the pres- 1 5 dihydroxynaphthalene ent invention arenondiscoloring. They stabilize Iiydmquinone both the uncured copolymerand the vulcanizate. Resorcinol They therefore advantagemtsly added Thestannous salts used in the preparation of in tantiatestarter:an; gg eg gg f g ggf 5 1 e gg a icuesa os o1e,sanus r- 3 ggi gg j g gg fi gi g giggf figgz mide, stannous sulfate, stannous benzene sulfonate, stannoustoluene sulfonate, stannous treatment naphthalene sulfonate, etc.

The tin complexes of this invention are pro- T f 11 X m 1 11 st t ducedby reacting stannous chloride or other gg g ggg i f z gf 1 u rate heplep phenolic compound, and alkali in solution. They EXAMPLE 1 arelight-colored and, therefore, contain no tin oxide which is a blackcompound. They con- STANNOUS COMPLEX 0F PHENOL tain more tin thancalculated for the tin salt of the phenolic compound. Their structure isunknown. They may be tin oxide polymers stabilized by the phenoliccompound having a Twenty grams of sodium hydroxide were dissolved in 200cubic centimeters of water, and then 47 grams of phenol were dissolvedin the resulting solution. A solution of 47.4 grams of formula such asROSn O sn 'O-sn0H' stannous chloride (anhydrous) in 100 cubic Where isan Q F residue one of the centimeters of water was added slowly duringmmal hydroxyls m thls Suggested molecule may stirring. The precipitatewas filtered, washed,

to some extent be replaced by chlorine or other and dried at The yieldwas 451) grams acid radical-depending upon the tin salt used Theprecipitate was white and when heated over in pr dufi the compleX- Thereis little fact an open flame it decomposed before melting. It t pp u h asuggested structure, and it underwent no apparent change on heating onemay be far from the actual structure. 50 hour at C. On analysis, ityielded 61.02

EXAMPLE 2 STANNoUs COMPLEX E BETA-NAI'HTHOL Seventy-two grams ofbeta-naphthol were dissolved in one liter of methanol, and to this wasadded a solution of grams of sodium hydroxide in 200 cubic centimetersof water. A solution of 47.4 grams of stannous chloride in 100 cubiccentimeters of per cent ethanol was then added slowly during stirring.The product was filtered and washed twice with alcohol. It was dried andfound to weigh 43.3 grams. It was a light-cream-colored powder whichdecomposed before melting on heating to a high temperature. It underwentno apparent change when heated one hour at 150 C. A tin analysis showedit'to contain 67.10 per cent tin. The calculated tin content of thenormal salt is 29.3 per cent.

EXAMPLE. 3

STANNOUS COMPLEX OF BETA-NAPHTHOL content was 73.10 per cent. Thecalculated tin content for the normal salt is 29.3%.

EXAMPLE 4 STANNOUS COMPLEX OF Q-CHLOROPHENOL Sixty-four and one-quartergrams of o-chlorophenol were dissolved in a solution of 20.6 grams ofsodium hydroxide in 200 cubic centimeters of water. A solution of 47.4grams of stannous chloride (anhydrous) in 100 cubic centimeters of waterwas added to this. An oily precipitate settled to the bottom. It waswashed by decantation and then separated from the water and dried. Itwas a white solid which decomposed before melting on heating to a hightemperature over an open flame but, apparently, was stable when heatedone hour at 150 C. The yield was grams. It was found by analysis tocontain 53.45 per cent tin. The calculated tin content of the normalstannous salt is 31.8%.

EXAMPLE 5 STANNOUS COMPLEX or P-PHENYLPHENOL One hundred and seventygrains of p-phenylphenol were dissolved in one liter of 95 per centethanol. A solution of 40 grams of sodium'hydroXide in 300 cubiccentimeters of water was then added. A solution of 94.8 grams ofstannous chloride (anhydrous) in 50 per cent ethanol was added tothe'former solution slowly during stirring. The resulting precipitatewas filtered, washed twice with 500 cubic centimeter portions of alcoholand once with water. The yield of dried product was 83 grams. It was avery light 4 yellow solid which decomposed on heating to a hightemperature on a spatula. It was, apparently, stable when heated onehour at 150 C. It was found to contain 64.15 per cent tin. Thecalculated tin content of the normal stannous salt is 25.9 per cent. Thechlorine content was .36 per cent.

EXAMPLE 6 STANNOUS COMPLEX or P-CYoLoHEXYLPHENoL An alcohol-watersolution of 52.8 grams of p-cyclohexylphenol and 24.0 grams of sodiumhydroxide was prepared. To this was added, with stirring, a solution of56.8 grams of stannous chloride (anhydrous) in alcohol. The precipitatewas filtered and then washed with alcohol and water. The yield was 52.0grams. The cream-colored product decomposed before melting when heatedover an open flame. It underwent no apparent change when heated one hourat 150 C. It contained 75.85 per cent tin and 10.3 per cent chlorine.tent for the normal salt is 25.3 per cent.

The ortho-dihydroxyphenols, such as catechol, form a compound analyzingclose to the normal stannous salt when reacted with equivalent amountsof stannous chloride and alkali. However, the other polyhydroxy aromaticcompounds, such as resorcinol, etc., form complexes which are muchhigher in tin than the normal salt. The following example isillustrative:

EXAMPLE 7 STANNOUS COMPLEX 0F HYDROQUINONE Fifty-five grams ofhydroquinone and 112.8 grams of stannous chloride dihydrate weredissolved in one liter of water. A solution of 40 grams of sodiumhydroxide in 150 cubic centimeters of water was slowly added until thesolution was alkaline. This required about 75 per cent of the solution.After stirring a short time, the product was filtered. The yield was 78grams. The product, a light-cream-colored solid, was, apparently,unchanged by heating one hour at 150 C. It decomposed on heating at ahigh temperature on a spatula. Analysis for tin showed it to contain70.45 per cent. It contained 14.75 per cent chlorine. The calculated tincontent for the normal salt is 52.3 per cent.

EXAMPLES 8-13 STANNOUS COMPLEXES 0F PHENoLs PREPARED BY FoLLowINoGENERAL METHOD The following general method was employed in producingstannous complexes of:

p-Tertiary-octylphenol p-Cyclohexylphenol p-Tertiary-butylphenolPetroleum cresylic acid 4,6-di-tertiary-butyl-m-cresol2,6-di-tertiary-butyl-p-cresol Three-tenths of a mol of sodium hydroxide(dissolved in water) was added to .3 mol of the phenol dissolved in percent ethanol. Then .15 mol (28.4 grams) of anhydrous stannous chloridein The calculated tin conof the stannous complexes may be given asreaction of the stannou salt with a phenolic compound and up to theequivalent amount of alkali.

6 temperatures. The table not only shows that the stabilizers arenondiscoloring but also shows that there was no appreciable change inthe physical properties of the copolymer on aging.

The amount of phenolic compound used may be 5 The control containingphenyl-beta-naphthylvaried over wide limits, and there is no harm amineshowed some deterioration. The data in in using a large excess (muchgreater than one the table consist of an observation of the colormolecular equivalent) and as little as 0.5 molecuand the results of ahand test. This hand test lar equivalent of the phenol. Examples 3 and 6consisted of pulling and feeling the copolymer illustrate the use ofless than a molecular equiva- 10 sample to detect any stiffening,softening or lent of phenol. Perhaps less than 0.5 molecular other signsof deterioration. Tests recorded for equivalent of the phenol would besufficient if the material aged 4 days include a test on the conditionswere properly controlled because only Firestone extrusion plastometerdescribed in a small amount of phenolic material is combined Dillon etal. 2,045,548. The figures given are the in the tin complex. Thereshould be at least subnumber of seconds required to extrude aconstantially one molecular equivalent of alkali presstant volume ofrubber through a given openent for each molecular equivalent of thestannous ing by action of a piston activated by a constant salt.pressure of 4%; pounds steam at a constant tem- It is preferable to usea solvent that is a solvent perature of 185 F.

Table I COPOLYMER AGING Condition After Drying Alter Four Days at 90 C.After Two Days at 120 C. Antioxidant Color Hand Test T454 Color HandTest Color Hand Test stannous complex of phenol white no deterioration.8.0 light brown unchanged. light brown unchanged. stannouls complex ofo-chlorodo do 8:0 do r10 .110 Do.

pneno stargnous complex of p-phenyl- .do ,.....do 6.0 verylight brown.do ..do Do.

p euo phenfil-beta-naphthylamine (conbrown... d0 5.6 brovm "do"... darkbrown. somewhat set up.

tro

GR-S, cured or uncured, when exposed to heat Table II COPOLYMER AGINGThe data in the above table show the stannous complexes to be equal tophenyl-beta-naphthylamine on aging at C. and superior on aging at C. Incolor, all of the samples containing the stannous complexes are quitesuperior to those containing phenyl-beta-naphthylamine. ihe samples wereall coagulated from the copolymerization emulsion mixture by the use ofaluminum sulfate low in iron.

The next table compares the stabilizing effect of several of thecomplexes with that of phenylbeta-naphthylamine when mixed with theemulsion resulting from the copolymerization reaction. Two percent ofthe stabilizer was used in each case.

Antioxidant Condition After Drying, Color and Hand Test Alter Aging 2Days at 90 0., Color and Hand Test After Aging 4 lfiays at 90 0., Colorand Hand lcst stannous complex of beta-naphthol (prepared according tothe process of Example 2).

stannous complex of beta-naphthol (prepared according to the process ofExample 3).

stannous complex of 4,6-di-tertiary-butyl-m-cresolphenyl-beta-naphthylamine cream color; no deterioration light yellow; nodeterioration light red-brown; no deterioration cream color; unchanged.light yellow; unchanged.

do cream color; unchanged.

light brown; unchanged.

light brown; unchanged. brown; unchanged brown; somewhat set up.

They stabilize without ape5 The results recorded in the above table.show the tin complexes to be superior to the control stabilizer,phenyl-beta-naphthylamine, on drying and under both conditions of aging.

It was found that a mixture of a phenolic compound and the stannouscomplex gave results somewhat superior to the use of either one alone.For convenience, the tests refer to mixture of a complex and the phenolfrom which the complex is prepared, but other phenols may be used.Stabilizing mixtures of phenols and complexes .75 are illustrated in.the following tablezw Table III OOPOLYMER AGING Antioxidant After DryingHours at 75 0., Color and Hand Test After Aging 4 Days at 90 0.,

After Aging 1 Day at 120 0., Color and Hand Test Color and Hand Test 2%2,G-di-tertiary-butyl-p-cresol 2% stannous complex of2,6-di-tertiarybutyl-p-cresol.

1% 2,6-di-tertiary-butyLp-cresol-l-1% stannous complex of same.

2% stannous complex of beta-naphthoL.

1% beta-naphthol+1% stannous complex of same.

beta-naphthol very light brown; no deterioratron.

yellow; no deterioration light brown; no dcterioratiom...

very light brown; no deterioration. cream color; no deterioration lightcream; no deterioration.

orange-yellow; nnch anged light brown; set up. light yellow-brown;unchanged.

light brown; surface slightly resinous. light brown; unchanged lightbrown;unchanged.

light yellow; unchanged brown; surface somwhat resinous. cream;unchanged cream; unchanged.

brown; unchanged brown; somewhat set up.

The Bardol of the above formula is a coal-tar plasticizer.

In the following table tests on the physical properties of differentvulcanizates are recorded. The values are averages of those obtained onTable IV COPOLYMER AGING 2% stannous com- 27 phenyl-betag ggnaphthylamine 2% Smut Condition after drying 20 hours at 75 (3.:

T lfl 37.0 7.8 8.0.

light cream brown green-gray. no deterioration". no deterioration... nodeterioration.

. light brown. brown.

unchanged slightly set up.

52.8 309.6. light brown. brown. unchanged set up.

The above data show that the stannous complex of hydroquinone issuperior to phenyl-betanaphthylamine as a stabilizer for the uncuredcopolymer and show a definite superiority of the stannous complex ascompared with Stalite (heptylated diphenylamine), a widely usedstabilizer for (313-5.

The stabilizers were compounded with vulcanizing ingredients accordingto two formulae. In one formula channel black was used, and the resultsof the test with this formula show the effect of the presence of thestabilizer in an ordinary stock. The other formula contains no black andis heavily loaded with zinc oxide, titanium dioxide, and Calcene (afinely divided calcium carbonate supplied by Pittsburgh Plate GlassCompany). Tests with this latter stock show the stabilizers of thisinvention to be nondiscoloring. In both formulae, GR-S copolymer wasemployed to which 2 per cent of the various stabilizers was added whilethe coploymer was still in the form of latex and before coagulation anddrying.

Formula I C; Moiocnwwwo stock cured 60 and minutes, respectively, at

Table V PROPE R'IIES OF VULCANIZATION stannous complex of p-phenylphenolPhenyl-betanaphthylamine Tensile:

Normal Aged Percent of Normal 69. 4 59. l Elongation:

Normal Aged Percent of Normal The above data show that the stabilizerused gives retention of modulus, tensile, and elongation on aging whichis comparable to that given by the widely approvedphenyl-beta-naphthylamme.

A further test was run to compare the stabilizing effect of a differentstabilizer with that of phenyl-beta-naphthylamine. Two per cent of eachstabilizer was employed. The values recorded are the average of curesmade at 280 F. for 80 and 120 minutes, respectively.

Table VII The results show that the stannous complex is superior tophenyl-beta-naphthylamine from the standpoint of modulus retention andabout equivalent in tensile and elongation retention.

In compounding the GR-S for tests in white stock, 2 per cent of variousstabilizers was added to latex of GR-s copolymer before coagulation. Thedried copolymer was then compounded as follows:

Formula II Copolymer+stabilizer 100 Stearic acid 1 Paraifin wax 0.5Calcene 50 Zinc oxide 5 Titanium dioxide 8 Sunproof wax 1.8 Green dye 2Cumar 2.5 Accelerator #1 1.3 Accelerator #2 0.1 Sulfur 1.5

The Calcene is finely divided calcium carbonate produced by PittsburghPlate Glass Company. Accelerator #1 is cyclohexyl benzothiazylsulfenamide. Accelerator #2 is tetramethylthiuram disulfide.

Samples of the white vulcanizate were cured 280 F. for 30 and 60minutes, respectively, and

then exposed in a fadeometer for 24 hours at F. with the followingresults:

Table VIII VULCANIZATE AGING Color of Aged Antloxldent Vulcanizate 2%stannous complex ofp-phenylplienoL. slightly discolored.

1% 2,6 ditertiary butyl p cresol+1% stannous complex of same.

1% beta-naphthol+l% stannous complex of same.

2% stannous complex of hydroquinone..

2% hcptylated' diphenylamine (contr0l).

di-beta-naphthyl-p-phenylene diamine' (control).

very slightly discolored.

slightly discolored.

Do. light brown. very dark brown.

The recorded results show that the stabilizers of this inventiondiscolor only slightly as com-- pared with two different commercialstabilizers and that the stabilizers of this invention. may, therefore,be classified as nondiscoloring.

The foregoing is illustrative. The stannous complexes may be used aloneor with a phenol. The stabilizers may be used not only for thestabilization of GPv-S and other copolymers of conjugated diene monomerand vinyl monomer, but also natural rubber, etc. They may be added tothe latex or compounded on the mill with dried latex coagulum or crepe,etc. They have particular value as nondiscoloring stabilizers for whiteGR-S or other copolymer of a conjugated diene monomer and a vinylaromatic monomer.

This application is a division of my co-pending application Serial No.85,473 filed April 4, 1949, now Patent No. 2,626,954 which. claims theStan nous complexes and their preparation.

What is claimed is:

l. The method of curing rubberlike copolymer of a conjugated dienemonomer and a vinyl aroniatic monomer without substantial discolorationwhich comprises heating the same with vulcanizing ingredients includingsulfur and as stabilizer a stannous complex of a phenolic compoundproduced by reaction of the stannou: it of a strong acid, an alkali anda phenolic cempound of the class which consists of monohydroxy aromaticcompounds and polyhydroxy aroma compounds except those which containortho hydroxy groups, which complex contains more tin than the normalstannous salt of the phenolic compound.

2. The method of drying rubber-like coaguluin of copolymer of butadieneand styrene without substantial discoloration which comprises heatingthe same while it contains admixed therein sulfur and as stabilizer astannous complex of a phenolic compound produced by reaction of thestannous salt of a strong acid, an alkali and a phenolic compound of theclass which con.- sists of monohydroxy aromatic compounds andpolyhydroxy aromatic compounds except those which contain ortho hydroxygroups, which complex contains more tin than the stannous salt of thephenolic compounds.

3. Dried coagulum of rubber-like copolymer of butadiene and styrenewhich contains as a stabilizer a stannous complex of a phenolic compoundproduced by reaction of the stannous salt of a strong acid, an alkaliand a phenolic com.- pound of the class which consists of monohydroxyaromatic compounds and polyhydroxy aromatic compounds except those whichcontain ortho hydroxy groups, which complex contains more tin than thestannous salt of the phenolic compound.

4. Latex of a rubber-like copolymer of conjugated diene monomer andvinyl aromatic monomer which contains as a stabilizer a stannous complexof a phenolic compound produced by reaction of the stannous salt of astrong acid, an alkali and a phenolic compound of the class whichconsists of monohydroxy aromatic compounds and polyhydroxy aromaticcompounds except those which contain ortho hydroxy groups, which complexcontains more tin than the stannous salt of the phenolic compound.

5. The method of curing rubber and rubberlike copolymer of a conjugateddiene monomer and a vinyl aromatic monomer which comprises heating thesame with vulcanizing ingredients and as a stabilizer a stannous complexof a phenolic compound produced by reaction of a stannous salt of astrong acid, an alkali and a phenolic compound of the class whichconsists of monohydroxy aromatic compounds and poly hydroxy aromaticcompounds except those which contain ortho hydroxy groups, which complexcontains more tin than the normal stannous salt of the phenoliccompound.

6. A substance of the group consisting of rubher and rubber-likecopolymer of a conjugated diene monomer and a vinyl aromatic monomerstabilized with a stannous complex of a phenolic compound produced byreaction of a stannous salt of a strong acid, an alkali and a phenoliccompound of the class which consists of monohydroxy aromatic compoundsand polyhydroxy aromatic compounds except those which contain orthohydroxy groups, which complex contains more tin than the stannous saltof the phenolic compound.

No references cited.

1. THE METHOD OF CURING RUBBER-LIKE COPOLYMER OF A CONJUGATED DIENEMONOMER AND A VINYL AROMATIC MONOMER WITHOUT SUBSTANTIAL DISCOLORATIONWHICH COMPRISES HEATIANG THE SAME WITH VULCANIZING INGREDIENTS INCLUDINGSULFUR AND AS STABILIZER A STANNOUS COMPLEX OF A PHENOLIC COMPOUNDPRODUCED BY REACTION OF THE STANNOUSE SALT OF A STRONG ACID, AN ALKALIAND A PHENOLIC COMPOUND OF THE CLASS WHICH CONSISTS OF MONOHYDROXYAROMATIC COMPOUNDS AND POLYHYDROXY AROMATIC COMPOUNDS EXCEPT THOSE WHICHCONTAIN ORTHOHYDROXY GROUPS, WHICH COMPLEX CONTAINS MORE TIN THAN THENORMAL STANNOUS SALT OF THE PHENOLIC COMPOUND.